The present invention relates to a method for the control of the braking effect of a brake-slip-controlled hydraulic or pneumatic brake system for automotive vehicles, in particular for road vehicles, equipped with an auxiliary energy supply system, in which method the braking behavior will be determined by virtue of tranducers, wherein the measured values will be prepared, logically combined and processed, and wherein in the case of a control action taking place, i.e. on detection of an imminent locked condition, the pressure medium flow to the wheel brake cylinders will be shut off temporarily, pressure medium will be discharged from the wheel brake cylinders and returned into the pressure medium cycle. Upon re-acceleration of the wheel, renewed pressure rise will take place at the proper point of time. Brake systems for implementing this method are within the scope of the present invention.
In the prior art methods and brake systems which serve to prevent the locking of individual or all wheels (toward the end of ensuring driving stability and steerability of the vehicle even under unfavorable conditions, for example in the event of icy roads or aquaplaning or during panic stops) the velocity, deacceleration and acceleration of the individual wheels is measured, compared with the vehicle velocity or a suitable reference input, and signals are derived therefrom for control of the braking pressure variation. The behavior of the vehicle and the braked wheels, respectively, under differing practical conditions, such as road conditions, adhesion of the tires, static and dynamic load of the individual wheels, state of the tires and of the brakes, as well as the behavior of the brakes under the influence of dead times, interference values vary within wide ranges. Accordingly, complicated correlations between the measured values and appropriate controlled variables for the braking pressure variation will result. Further, the transducers are imperfect, and the processing of the measured signals is subject to inevitable disturbing influences. Brake-slip-controlled brake systems therefore are rather complicated.
Hence, the prior art systems deal with correlations between the measured signals and appropriate controlling and regulating measures as well as with the selection and design of sensors, evaluation circuits and braking pressure modulators.
For the purpose of simplification of the control apparatus and reduction of the manufacturing effort, it has been proposed to control individual wheels or one axle only, while the remaining wheels are acted upon by the same amount of braking pressure or by braking pressure derived from the controlled wheels or by uncontrolled braking pressure (European patent application EU-PA 51 801). Overbraking and locking of individual wheels under specific conditions. In such systems in comparison to vehicles where all wheels are controlled, a loss of steerability, a longer stopping distance or unstable driving conditions results.
It is an object of the present invention to propose a method for control of the braking effect, which method allows to be implemented in a simple brake system entailing comparatively little manufacturing effort and which guarantees nevertheless the driving stability of the vehicle will be maintained during the braking operation under all conditions and that effective braking will be accomplished.